The invention relates to a linear drive with a pneumatic, hydraulic or electric actuator cylinder, whose piston rod is fixed in position, and whose moving cylinder, that is guided in the lengthways direction, forms a supporting and driving part of a stroke ratio changing transmission. The transmission changes the ratio of the relative motion between the cylinder and its lengthways guide means and transmits it to a linearly moving drive output member.
In a prior art linear drive the drive output member is moved by pneumatic, hydraulic or electrical power. The driving effect is produced by an actuator cylinder that is fixed to the housing of the linear drive. A stroke ratio changing transmission is joined with the end of the moving piston rod, such transmission causing the drive output member to be moved with twice the stroke of the piston. In this design the known idea on which the stroke ratio changing effect is based is that of using two driven toothed belts, placed at the sides of the piston rod so that they are on the one hand fixed to the housing and on the other to the drive output member, such belts running over two pairs of pulleys that are fixedly joined together by pulley support means coupled with the piston rod of the cylinder. Placing the stroke ratio changing transmission on the moving piston rod makes for a complex design that takes up much space to make certain that there are no sideways forces or moments acting on the piston rod, more specially when it has been moved outwards, such forces otherwise being likely to be the cause of the piston rod jamming, for example.
This condition exists in the known, complex design noted here in that there are two pulley supports placed symmetrically in relation to the axis of the piston rod so that the resultant force produced from the separate forces takes effect in the direction of the piston rod axis.